Deformation and fluid flow in the Munsiari Thrust (NW India): A preliminary fluid inclusion study

Deformation and fuid flow in the Munsiari Thrust (NW India): a preliminary fluid inclusion study. A fluid inclusion study was carried out on quartz veins deformed during the activity of the Munsiari Thrust in the Garhwal Himalaya (NW India, Western Himalaya). These veins are hosted in mylonitic phyllites, with a greenschist mineral assemblage made of quartz-white mica-biotite-chlorite-epidote and minor calcite and plagioclase. Within the veins two groups of isolated "early fluid" inclusions and trails of small secondary fluid inclusions have been observed. Two types of inclusions preserved in isolated groups have been petrographycally recognized: (i) a two liquids and a vapor phase (L1+L2+V) that is the most common type and (ii) a less frequent liquid and a vapor phase (L+V). Both types of fluid inclusions were investigated through optical microthermometric experiments. For "early fluid" inclusions, assuming a trapping temperature based on quartz dynamic recrystallization mechanisms and previous P-T estimates, in the range of 500-520°C, a corresponding trapping pressure in the range of c. 0.50-0.53 GPa is estimated. The trapping pressure range evaluated in the present contribution support that these fluid inclusions have been entrapped during the early stages of the activity of the Munsiari Thrust.